Use the Best Sources
To define your topic you may have been using some sources already- encyclopedias, text books, magazines, newspapers, web sites, etc. Now, you need to find information to help build your knowledge of the topic and provide the 'evidence' for what you write.
There are two aspects of information sources to keep in mind:
Your instructor may have specific requirements for the sources you use in your bibliography but you will use many more sources to inform yourself and provide context for your writing.
Information has a lifespan; it changes, grows and shows up in different types of publications throughout its life. Understanding the Information Timeline will help you determine which types of publications will be most appropriate for you to use at various points in your research.